The long-term objective of the proposed research are to understand the neural mechanisms of visual processing, how those mechanisms change, throughout life, and how they are altered to compensate for brain damage. Two specific projects are proposed for the renewal period. The first will continue our investigations of the mechanisms of neural compensation that occurs following visual cortex (VC) damage early in life. Anatomical studies will be carried out in cats to learn more about retinal inputs to the central visual pathways after VC damage, to investigate the nature and mechanisms of enhanced projections that develop from the lateral geniculate nucleus (LGN) to posteromedial lateral suprasylvian (PMLS) cortex following VC damage at different ages, and to determine whether other enhanced projections exist. We also will begin to investigate the biochemical bases of the compensation that occurs following early VC damage. Immunohistochemical studies of the distribution of nerve growth factor (NGF) receptors during normal development and after VC damage will be carried out to learn more about why there is greater potential for compensation in neonates than adults. In addition, we will investigate whether compensation can be increased by administering trophic factors. Together, these experiments will provide information about the mechanisms of recovery from brain damage and possible treatments to improve recovery. The second project will extend our previous work on early visual system development to include changes that occur during aging. Neurophysiological and anatomical studies will be carried out in the retina, LGN, and striate cortex of young adult and old monkeys. The results will be related to changes in human psychophysics during aging, and they will be used to test directly several hypotheses that have been proposed concerning the location and nature of the neural changes that underly vision deficits during aging. These studies will increase our understanding of the relationship between neural structure and function, of the neural mechanisms of declines in visual abilities during aging, and of the affects of aging on the brain in general.